SYNTHESIS, CHARACTERIZATION AND BIOMIMETIC OXYGENATIONS OF MANGANESE(II), IRON(III) AND COPPER(II) PYRIDYL HYDRAZONE COMPLEXES

The preparation and characterization of Mn-II, Fe-III and Cu-II comple xes of three tridentate pyridyl hydrazones are reported. The ligands w ere prepared via Schiff base condensation of 6-chloro-2-hydrazopyridin e with alpha-formyl-(L-1), alpha-acetyl-(L-2), or alpha-benzoyl-(L-3) pyridine. The structural characterization of the compounds prepared wa s based on elemental analyses, electrical conductance and magnetic mom ent measurements, H-1-n.m.r., i.r., u.v.-vis. and e.s.r spectroscopic methods. The overall structure and reactivity of the metal chelates cr itically depend on the ligand substituents within the carbonyl moiety. Octahedral and tetrahedral monomeric species were proposed for Mn-II complexes, and an octahedral environment for the Fe-III complexes. Reg arding the copper(II) complexes, a monomeric square-planar and a dimer ic structure with a chloride bridge in square-pyramidal geometry were suggested. In the presence of molecular oxygen, Mn-II and Cu-II comple xes catalyse the oxidative transformation of catechol (benzene-1,2-dio l) to the corresponding o-benzoquinone. Iron(III) complexes catalyse t he aerobic oxidation of catechol to the intradiol cleavage product. Th e catalytic activity has been correlated with the Lewis acidity of the metal centres created according to the nature of the ligand substitue nts. The probable mechanistic implications of the catalysed oxidation reactions are discussed.